96 THE VITAL FUNCTIONS. 



sufficiently far to effect their consolidation into more com- 

 pact structures.* 



Fishes which live upon other animals of the same class 

 having a soft texture, are furnished with teeth constructed 

 merely for seizing their prey, and perhaps also for slightly di- 

 viding it, so as to adapt it to being swallowed. These teeth 

 are of various shapes, though usually sharp at the points, and 

 either conical or hooked at the extremity, with the points al- 

 ways directed backwards, in order to prevent the escape of the 

 animal which has been seized. Those fishes which subsist on 

 testaceous mollusca have teeth with grinding surfaces, and 

 their jaws are also adapted for mastication. Every part of the 

 mouth, tongue, and even throat, may afford lodgement for 

 teeth in this class of animals. Almost the whole cavity of the 

 mouth of the Jlnarrhichas lupus, or wolf-fish, may be said to 

 be paved with teeth, a triple row being implanted on each 

 -side; so that this fish exerts great power in breaking shells. 

 The Shark has numerous rows of sharp teeth, with serrated 

 margins: these, at first sight, appear to be formidable instru- 

 ments; but as the teeth in the opposite jaws do not meet, it 

 is evident that they are not intended for cutting, like the 

 incisors of mammalia. 



Among Reptiles we find the Batrachia almost wholly des- 

 titute of teeth. Frogs, indeed, exhibit two rows of very fine 

 points; the one in the upper jaw, and the other passing trans- 

 versely across the palate: they may be considered as teeth 

 existing in a rudimental state; for they are not sufficiently 

 developed to be useful in mastication. There are about 

 forty of these minute teeth on each side in the frog. In the 

 Salamander, there are sixty above and below; and also thirty 

 on each side of the palate. 



The tongue of the frog is of great length ; its root is at- 

 tached close to the fore part of the lower jaw, while its point, 



* Attempts have been made to trace analogies between the different seg- 

 ments of the jaws of fishes and corresponding parts of the mouths of crus- 

 tacea and of insects: but the justness of these analogies is yet far from being 

 satisfactorily proved. 



